battery

Abstract

This application provides a battery. The battery includes a casing, a cell assembly, and an adapter. The casing includes a receiving cavity. The cell assembly includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrode. The edges of two adjacent separators extend beyond the edge of the negative electrode to form a composite region. The length L1 of the composite region along a second direction is 0.3 mm ≤ L1 ≤ 2.2 mm. The positive electrode includes a positive current collector and a plurality of first tabs. The plurality of first tabs are stacked to form a positive electrode tab portion. The positive electrode includes a first positive electrode portion near a first wall of the casing. The first tab of the first positive electrode portion includes a first stacked section and a first connecting section. The connection between the first stacked section and the first connecting section forms a first bending point. The distance d1 between the edge of the negative electrode near the first bending point and the first bending point is 0.2 mm ≤ d1 ≤ 2 mm. L1 and d1 satisfy: 0.1 ≤ d1 / L1 ≤ 3. The battery of this application helps to reduce the risk of short circuits caused by contact between the negative electrode and the positive electrode tab portion.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more particularly to a battery. Background Technology

[0002] Lithium-ion batteries have been widely used in electric vehicles, energy storage systems, and portable electronic devices due to their high energy density, long cycle life, and low self-discharge rate. As users increasingly demand fast charging performance and high-rate discharge capabilities, the design of the current transport path within the battery has become one of the key factors affecting performance.

[0003] In related technologies, multiple sub-tabs are set on the current collector, and the multiple sub-tabs are stacked to form an integral tab part. Then, the tab part is connected to the adapter (such as an adapter plate, terminal post or busbar) to realize the connection between the battery and the external circuit, so as to improve the rate performance of the battery.

[0004] However, in some battery structure designs, the tabs formed by stacking multiple sub-tabs and the connecting parts all need to be bent along the thickness direction of the battery to fit the size of the casing or connect with other components, reducing their space occupation inside the casing. To ensure battery safety, the edge of the negative electrode is usually not set beyond the edge of the positive electrode. However, during battery use and safety testing, the tabs and connecting parts may shift or deform when subjected to external forces. This increases the risk of the positive electrode tab contacting the edge of the negative electrode, leading to a short circuit and reducing battery safety. Summary of the Invention

[0005] This application provides a battery in which a separator forms a composite region covering the end of the negative electrode sheet, while limiting the gap between the negative electrode sheet and the positive electrode tab, which helps to reduce the risk of short circuits caused by contact between the negative electrode sheet and the positive electrode tab.

[0006] This application provides a battery, including: a casing and a cell assembly. The casing includes a receiving cavity for accommodating the cell assembly. The casing includes a first wall and a side wall surrounding the first wall, which together form the receiving cavity. Along a first direction, the casing also includes a second wall disposed opposite to the first wall. The cell assembly includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrode. Along the first direction, the separator is disposed on both sides of the negative electrode. Along a second direction, the edges of two adjacent separators extend beyond the edge of the negative electrode. At least a portion of the edges of adjacent separators are bonded together to form a composite region. The length L1 of the composite region along the second direction satisfies: 0.3mm ≤ L1 ≤ 2.2mm. The positive electrode includes a positive current collector and a plurality of first tabs extending outward from one side of the positive current collector. A positive electrode tab is formed by stacking two first electrode tabs. The positive electrode tab is bent towards a first wall along a first direction. Along the first direction, the positive electrode sheet includes a first positive electrode sheet portion near the first wall. The first electrode tab of the first positive electrode sheet portion includes a first stacked segment and a first connecting segment connected to the first stacked segment. Along the second direction, the first connecting segment is located on the side of the first stacked segment away from the positive current collector. A first bending point is formed at the connection between the first stacked segment and the first connecting segment. Along the second direction, the distance d1 between the edge of the negative electrode sheet near the first bending point and the first bending point satisfies: 0.2mm≤d1≤2mm. An adapter is formed by bending a second connecting segment and a third connecting segment. The first connecting segment is connected to the second connecting segment, and the third connecting segment extends out of the housing. Wherein, L1 and d1 satisfy: 0.1≤d1 / L1≤3.

[0007] The battery provided in this application embodiment forms a positive electrode tab by stacking a plurality of first tabs on the positive electrode sheet, which increases the conductive cross-sectional area, shortens the current conduction path, and reduces the internal resistance, thereby improving the rate performance and fast charging capability of the battery; in order to reduce the space occupied by the battery head, the positive electrode tab and the adapter are bent, thereby improving the energy density of the battery.

[0008] When the battery is subjected to external forces such as heat pressure or drops, the external force is transmitted to the positive electrode tab through the adapter, causing the positive electrode tab to shift towards the cell assembly. By forming a composite region that covers the negative electrode sheet with the portions of two adjacent separators protruding from it, the insulation performance at the end of the negative electrode sheet is improved. At the same time, the length L1 of the composite region is further limited to: 0.3mm ≤ L1 ≤ 2.2mm. On the one hand, this avoids a composite region that is too small, resulting in weak adhesion between the protruding portions of the two adjacent separators, making them prone to separation during battery expansion and providing little physical separation. Furthermore, if the positive electrode tab shifts or deforms, it will squeeze and laterally push the composite region. If the composite region is too small, the two separator layers in the composite region may misalign or shrink after being squeezed, leading to exposure of the negative electrode edge and increasing the risk of contact with the first electrode tab of the first positive electrode sheet. On the other hand, the composite region... If the length of the first electrode is too large, in order to ensure that the first electrode extends sufficiently beyond the diaphragm so that multiple first electrodes can be stacked to form the positive electrode and connect to the adapter, the design length of the first electrode will increase accordingly. After the positive electrode is bent, a large number of redundant areas of the first electrode are formed between the first bending point and the cell assembly along the first and second directions. During the drop, the redundant areas of the positive electrode have a large degree of freedom of deformation, making it easier to squeeze the cell assembly, contact the edge of the negative electrode, or cause the sharp edge of the first electrode to pierce the diaphragm and contact the edge of the negative electrode, resulting in a short circuit.

[0009] Furthermore, since the hardness of the adapter is greater than that of the first tab, after the positive tab bends towards the first wall, the first tab of the first positive electrode is furthest from the adapter. When the external force on the adapter is transmitted to the positive tab, the first tab of the first positive electrode has the greatest degree of freedom in deformation or displacement. Therefore, after the positive tab is offset, the first bending point of the first tab of the first positive electrode is closest to the edge of the negative electrode, and the risk of it contacting the edge of the negative electrode is the greatest. Therefore, by limiting the distance d1 between the first bending point of the first tab on the first positive electrode and the negative electrode to satisfy: 0.2mm≤d1≤2mm, the risk of short circuit between the first tab connected to the first positive electrode and the negative electrode is reduced. On the one hand, it avoids the distance between the first bending point and the negative electrode sheet being too close, and the distance between the first tab of the first positive electrode sheet and the negative electrode sheet being too small, which increases the risk of the negative electrode sheet extending and contacting the aforementioned first tab when the battery expands, leading to a short circuit. On the other hand, it avoids the distance between the first bending point and the negative electrode sheet being too large, which would increase the space occupied by the positive electrode tab on one side in the second direction, reducing the energy density of the battery. At the same time, an excessively large distance between the first bending point and the negative electrode sheet may exert a certain pulling force on a certain layer of the first tab in the positive electrode tab, increasing the risk of the first tab breaking when subjected to external impact.

[0010] Furthermore, limiting d1 / L1 to a suitable range serves two purposes. Firstly, it avoids d1 / L1 being too small, which would result in either d1 being too small or L1 being too large, causing the first bending point to be too close to the negative electrode, increasing the risk of contact between them. Conversely, an excessively large L1 would increase the redundant size of the first tab, increasing the risk of the first tab deforming and contacting the edge of the negative electrode or puncturing the separator after a battery drop. Secondly, it avoids d1 / L1 being too large, which would increase the space occupied by the positive electrode tab and the adapter within the battery, leading to a decrease in energy density. Alternatively, an excessively large d1 / L1, coupled with a small L1, would decrease the bonding stability between the separators in the composite region, making it easier for the separators in the composite region to open during battery cycling or drop tests, exposing the negative electrode and increasing the risk of contact with the first tab. Thus, by keeping d1 / L1 within a suitable range, it is beneficial to improve the battery's energy density while reducing the risk of short circuits between the negative electrode and the first tab.

[0011] In some embodiments, an overlap area is formed between the first connecting segment and the second connecting segment, and a solder mark is provided on at least a portion of the overlap area; the length L2 of the overlap area along the length direction of the second connecting segment satisfies: 0.8mm≤L2≤4mm; and / or, the length L3 of the solder mark along the length direction of the second connecting segment satisfies: 0.3mm≤L3≤2mm; and / or, the included angle β between the second connecting segment and the third connecting segment satisfies: 70°≤β≤130°.

[0012] In some embodiments, a second bending point is formed between the second connecting segment and the third connecting segment; along the first direction, the distance between the first bending point and the side surface of the cell assembly near the second wall is H1, and the distance between the first bending point and the second bending point along the first direction is H2, where H1 < H2 and H2 - H1 ≤ 0.3 mm.

[0013] In some embodiments, along the first direction, the positive electrode includes a second positive electrode portion near the second wall, and the first tab of the second positive electrode portion includes a second stacked segment and a fourth connecting segment connected to the second stacked segment. Along the second direction, the fourth connecting segment is located on the side of the second stacked segment away from the positive current collector, and a third bending point is formed at the connection between the second stacked segment and the fourth connecting segment. Along the second direction, the interval between the third bending point and the edge of the negative electrode is d2, where 0.7≤d1 / d2≤1.3.

[0014] In some embodiments, at least one first electrode tab in the positive electrode tab portion includes a bending section, the bending section including a first bending segment and a second bending segment, the angle between the first bending segment and the second bending segment being α, 40°≤α≤180°.

[0015] In some embodiments, the positive electrode tab is connected to the adapter to form a current-guiding structure. The adapter is provided with an adhesive. Along the length direction of the current-guiding structure itself, the distance between the end of the third connecting segment near the cell assembly and the edge of the separator is L4. The thickness of the cell assembly along the first direction is T, where L4≤T.

[0016] In some embodiments, the negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a silicon-based material, and the mass content of silicon element in the negative electrode active layer is 5%-70%; and / or, the silicon-based material includes at least one of silicon-carbon composite material and silicon-oxygen composite material.

[0017] According to some embodiments of the present invention, the volume average particle size Dv50 of the silicon-based material is 2μm-15μm.

[0018] According to some embodiments of the present invention, the sphericity of the silicon-based material is 0.7-1.

[0019] In some embodiments, the positive electrode, the negative electrode, and the separator are wound to form the battery cell assembly. The positive electrode has a first surface facing the winding center of the battery cell assembly and a second surface facing away from the winding center of the battery cell assembly. The first surface is provided with a first positive active layer, and the second surface is provided with a second positive active layer. The areal density of the first positive active layer is N1, and the areal density of the second positive active layer is N2, where 0.89 ≤ N1 / N2 ≤ 0.99. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0021] Figure 1 This is a schematic diagram of the internal structure of the battery according to an embodiment of this application;

[0022] Figure 2 This is a partial structural diagram of the battery's internal structure according to an embodiment of this application;

[0023] Figure 3 This is a schematic diagram of the membrane forming composite region according to an embodiment of this application;

[0024] Figure 4 This is a schematic diagram of the current guiding structure on the battery cell assembly according to an embodiment of this application unfolding along the second direction;

[0025] Figure 5 This is a schematic diagram of a wound battery cell assembly according to an embodiment of this application.

[0026] Figure label:

[0027] 110 - Shell; 110a - Receiving cavity; 111 - First wall; 112 - Second wall;

[0028] 120 - Cell assembly; 121 - Positive electrode sheet; 121a - First positive electrode sheet portion; 121b - Second positive electrode sheet portion; 121c - First surface; 121d - Second surface; 121e - First positive electrode active layer; 121f - Second positive electrode active layer; 1211 - Positive electrode current collector; 1212 - First tab; 1212a - First stacked segment; 1212b - First connecting segment; 1212c - First bending point; 1212d - Second stacked segment; 1212e - Fourth connecting segment; 1212f - Third bending point;

[0029] 122-Negative electrode;

[0030] 123 - Diaphragm; 1231 - Composite zone;

[0031] 130 - Adapter; 131 - Second connecting section; 1311 - Overlapping area; 1312 - Solder mark; 132 - Third connecting section; 133 - Second bending point; 134 - Adhesive component.

[0032] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0033] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0034] Lithium-ion batteries have been widely used in electric vehicles, energy storage systems, and portable electronic devices due to their high energy density, long cycle life, and low self-discharge rate. As users increasingly demand fast charging performance and high-rate discharge capabilities, the design of the current transport path within the battery has become one of the key factors affecting performance.

[0035] In related technologies, multiple sub-tabs are set on the current collector, and the multiple sub-tabs are stacked to form an integral tab part. Then, the tab part is connected to the adapter (such as an adapter plate, terminal post or busbar) to realize the connection between the battery and the external circuit, so as to improve the rate performance of the battery.

[0036] However, in some battery structure designs, the tabs formed by stacking multiple sub-tabs and the connecting parts all need to be bent along the thickness direction of the battery to fit the size of the casing or connect with other components, reducing their space occupation inside the casing. To ensure battery safety, the edge of the negative electrode is usually not set beyond the edge of the positive electrode. However, during battery use and safety testing, the tabs and connecting parts may shift or deform when subjected to external forces. This increases the risk of the positive electrode tab contacting the edge of the negative electrode, leading to a short circuit and reducing battery safety.

[0037] In view of this, the present application provides a battery in which a separator is formed to cover the end of the negative electrode sheet, while limiting the gap between the negative electrode sheet and the positive electrode tab, which helps to reduce the risk of short circuit between the negative electrode sheet and the positive electrode tab.

[0038] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will now be described with reference to the accompanying drawings.

[0039] For ease of explanation and understanding, the second direction can be the length direction of the battery, such as... Figure 1 The X direction shown can be either the thickness direction of the battery or, for example, the direction of thickness. Figure 1 The Z direction is shown.

[0040] refer to Figures 1 to 5 This application provides a battery, which includes a casing 110 and a cell assembly 120.

[0041] The housing 110 includes a receiving cavity 110a for accommodating the battery cell assembly 120. The housing 110 includes a first wall 111 and a side wall surrounding the first wall 111. The first wall 111 and the side wall surrounding the first wall 111 together form the receiving cavity 110a. Along a first direction, the housing 110 also includes a second wall 112 disposed opposite to the first wall 111. Exemplarily, the first wall 111 and the side wall are formed as a frame structure with a top opening, and the second wall 112 is located at the top of the frame structure, forming a sealed housing 110.

[0042] Alternatively, in other embodiments, the housing 110 may be integrally formed from aluminum-plastic film or metal sheet by stamping (forming) process, including a first wall 111 and a second wall 112 disposed opposite to each other along a first direction, and a surrounding side wall connecting the first wall 111 and the second wall 112, the three together forming a sealed space for accommodating the battery cell assembly 120. The first wall 111 and the sidewalls surrounding the first wall 111 are deep recessed surfaces formed by stamping. The degree of concavity along the first direction is relatively large, which is used to provide sufficient space for the bent positive electrode tab and the adapter 130 to accommodate and assemble. The second wall 112 is a shallow recessed surface. It can be stamped to form a shallow recessed surface, so that the depth of the concavity is less than that of the first wall 111 to accommodate part of the battery cell assembly 120. Alternatively, the second wall 112 can be left unstamped and covered over the opening of the receiving cavity 110a to cover the upper surface of the battery cell assembly 120 away from the first wall 111. The second wall 112, the first wall 111, and the sidewalls surrounding the first wall 111 can be integrally formed structures to accommodate, support, and seal the battery cell assembly and maintain the overall structural strength of the housing 110. This not only facilitates the efficient use of the battery's internal space, but also allows for precise adaptation of the tab bending path and the adapter 130 direction through differentiated design of the second wall 112 and the first wall 111. This ensures a safe distance between the tab and the negative electrode 122 within a compact layout, improves the battery's internal integration, and enhances the battery's safety and energy density.

[0043] refer to Figure 1 and Figure 3 The battery cell assembly 120 includes a positive electrode 121, a negative electrode 122, and a separator 123 disposed between the positive electrode 121 and the negative electrode 122. Along a first direction, separators 123 are disposed on both sides of the negative electrode 122 to separate the positive electrode 121 and the negative electrode 122.

[0044] Optionally, in this embodiment, the cell assembly 120 can be formed by stacking multiple positive electrode plates 121, separators 123 and negative electrode plates 122 to form a stacked cell, or the cell assembly 120 can also be formed by winding the positive electrode plates 121, separators 123 and negative electrode plates 122 to form a wound cell.

[0045] Along the second direction, the edges of two adjacent separators 123 extend beyond the edge of the negative electrode 122. For a laminated cell, the two adjacent separators 123 are the two separators 123 on either side of the negative electrode 122 along the first direction. For a wound cell, the two adjacent separators 123 are the two adjacent layers of separators 123 after winding. At least a portion of the edges of the adjacent separators 123 are bonded to form a composite region 1231. That is, along the second direction, the regions of the two adjacent separators 123 extending beyond the negative electrode 122 can be partially bonded to form the composite region 1231 (e.g., the edges of the two separators 123 are partially bonded, with the bonded area extending toward the negative electrode 122), or the entire regions of the two adjacent separators 123 extending beyond the negative electrode 122 can be bonded to form the composite region 1231.

[0046] The length L1 of the composite region 1231 along the second direction satisfies: 0.3mm≤L1≤2.2mm. For example, L1 can be 0.3mm, 0.6mm, 0.9mm, 1.2mm, 1.5mm, 1.8mm, 2.1mm or 2.2mm.

[0047] It should be noted that the composite region 1231 may be provided only at one end of the cell assembly 120 where the first tab 1212 extends, or the composite region 1231 may be provided at both ends of the cell assembly 120 along the second direction.

[0048] refer to Figure 1 and Figure 2 The positive electrode 121 includes a positive current collector 1211 and a plurality of first tabs 1212 extending outward from one side of the positive current collector 1211. The plurality of first tabs 1212 are stacked to form a positive electrode tab portion. When the cell assembly 120 is a stacked cell, a single positive electrode 121 may have one first tab 1212. There may be a plurality of positive electrode 121. When the plurality of positive electrode 121 are stacked, the first tabs 1212 on the positive electrode 121 are stacked to form a positive electrode tab portion. When the cell assembly 120 is a wound cell, a plurality of first tabs 1212 may be spaced apart on the positive electrode 121. When the positive electrode 121 is wound, the plurality of first tabs 1212 are stacked to form a positive electrode tab portion.

[0049] The positive electrode tab is stacked along the first direction and bent toward the first wall 111. In this way, the positive electrode tab also occupies a part of the space in the second direction, so as to avoid the positive electrode tab exceeding the thickness of the cell, thereby saving the head space of the battery and improving the energy density of the battery.

[0050] Along the first direction, the positive electrode 121 includes a first positive electrode portion 121a near the first wall 111. The first tab 1212 of the first positive electrode portion 121a includes a first stacked segment 1212a and a first connecting segment 1212b connected to the first stacked segment 1212a. Along the second direction, the first connecting segment 1212b is located on the side of the first stacked segment 1212a away from the positive current collector 1211. The connection between the first stacked segment 1212a and the first connecting segment 1212b forms a first bending point 1212c.

[0051] Understandably, since multiple first tabs 1212 are stacked to form a positive electrode tab, and the positive electrode tab bent towards the first wall 111 is welded to the adapter 130, in the final product structure, regarding the positive electrode tab, the stacking start position of each first tab 1212 is different. The stacked section of each first tab 1212 is close to the positive current collector, and the side of each first tab 1212 away from the positive current collector forms a connecting section, which is connected to the stacked section of each first tab. Specifically, the first stacked section 1212a corresponds to the front end of the stacking of the first tab 1212 on the first positive electrode sheet 121a, the first connecting section 1212b corresponds to the first stacked section 1212a of the first tab 1212 on the first positive electrode sheet 121a, and the first connecting section 1212b is connected to the adapter 130 to ensure the overcurrent capacity of the battery.

[0052] In this design, the positive electrode tab bends towards the first wall 111 along a first direction, forming a first bending point 1212c on the first tab 1212 of the first positive electrode sheet 121a, reducing space occupation and improving the energy density of the battery. That is, regarding the first tab 1212 on the first positive electrode sheet 121a, the first stacked segment 1212a is the part located between the first bending point 1212c and the cell assembly 120, and the first connecting segment 1212b is the part between the first bending segment 1212c and the end of the first tab 1212 (that is, the end away from the cell assembly 120).

[0053] It should be noted that for wound cells, the outermost part of the positive electrode 121 is generally a single-sided positive electrode area or a positive electrode empty foil area, without the first tab 1212. That is to say, in a wound cell, the first positive electrode portion 121a of the positive electrode 121 is not the outermost part of the positive electrode 121 that is closest to the first wall 111, but rather the part of the positive electrode 121 that is provided with the first tab 1212 and is closest to the first wall 111.

[0054] Understandably, when the positive electrode tab is bent, and a first bending point 1212c is formed on the first tab 1212 of the first positive electrode portion 121a, the area between the first stacked segment 1212a and the first connecting segment 1212b where the first bending point 1212c is located is formed into an arc-shaped area (approximately a U-shaped or C-shaped structure). In a specific example, the opening of the arc-shaped area where the first bending point 1212c is located can face the second wall 112.

[0055] Along the second direction, the distance d1 between the edge of the negative electrode 122 near the first bending point 1212c and the first bending point 1212c satisfies: 0.2mm ≤ d1 ≤ 2mm. For example, d1 can be 0.2mm, 0.6mm, 1mm, 1.4mm, 1.8mm, or 2mm. Of course, d1 can also be other sizes, and this application does not limit this.

[0056] The adapter 130 includes a second connecting segment 131 and a third connecting segment 132 formed by bending. That is, the adapter 130 is also bent, and the second connecting segment 131 and the third connecting segment 132 are formed in a U-shape, L-shape, V-shape or C-shape, without any specific limitation. The first connecting segment 1212b is connected to the second connecting segment 131, and the third connecting segment 132 extends out of the housing 110 to realize the circuit conduction between the cell assembly 120 and the outside world.

[0057] Wherein, L1 and d1 satisfy the condition: 0.1 ≤ d1 / L1 ≤ 3. For example, d1 / L1 can be 0.1, 0.5, 1, 1.5, 2, 2.5 or 3. Preferably, 0.5 ≤ d1 / L1 ≤ 2. Of course, d1 / L1 can also be other values, and this application does not limit them.

[0058] The battery provided in this application embodiment forms a positive electrode tab by stacking a plurality of first tabs 1212 on the positive electrode sheet 121, which increases the conductive cross-sectional area, shortens the current conduction path, and reduces the internal resistance, thereby improving the rate performance and fast charging capability of the battery; in order to reduce the space occupied by the battery head, the positive electrode tab and the adapter 130 are bent, thereby improving the energy density of the battery.

[0059] When the battery is subjected to external forces such as heat pressure or drop, the external force is transmitted to the positive electrode tab through the adapter 130, causing the positive electrode tab to shift towards the direction closer to the cell assembly 120; by forming a composite region 1231 by making the portions of two adjacent separators 123 protrude from the negative electrode 122 to cover the negative electrode 122, the insulation performance of the end of the negative electrode 122 is improved. Meanwhile, the length L1 of the composite region 1231 is further limited to satisfy: 0.3mm≤L1≤2.2mm. On the one hand, this avoids the composite region 1231 being too small, resulting in weak adhesion between the protruding parts of the two adjacent separators 123, making them prone to separation during battery expansion and thus providing little physical separation. Additionally, if the positive electrode tab shifts or deforms, it will squeeze and laterally push the composite region 1231. If the composite region 1231 is too small, the two separators 123 in the composite region 1231 may easily become misaligned or shrink inward after being squeezed, leading to exposure of the negative electrode edge and increasing the risk of contact with the first electrode tab 1212 of the first positive electrode sheet. On the other hand, if the length of the composite region 1231 is too large... To ensure that the first tab 1212 extends sufficiently beyond the diaphragm 123 so that multiple first tabs 1212 are stacked to form a positive tab that connects to the adapter 130, the design length of the first tab 1212 is correspondingly increased. After the positive tab is bent, a large number of redundant areas of the first tab 1212 are formed between the first bending point 1212c and the cell assembly 120 along the first and second directions. During the drop, the redundant areas of the positive tab have a large degree of freedom of deformation, making it easier to squeeze the cell assembly 120 and contact the edge of the negative electrode 122. Alternatively, the sharp part of the edge of the first tab 1212 may pierce the diaphragm 123 and short-circuit with the negative electrode 122.

[0060] Furthermore, since the hardness of the adapter 130 is greater than that of the first tab 1212, after the positive tab bends towards the first wall, the first tab 1212 of the first positive electrode portion 121a is furthest from the adapter 130. When the external force on the adapter 130 is transmitted to the positive tab, the deformation or offset degree of freedom of the first tab 1212 of the first positive electrode portion 121a is the greatest. Therefore, after the positive tab is offset, the risk of it contacting the edge of the negative electrode 122 is the greatest. Thus, by limiting the distance d1 between the first bending point 1212c of the first tab 1212 on the first positive electrode portion 121a and the negative electrode 122 to satisfy: 0.2mm≤d1≤2mm, the risk of short circuit between the first tab 1212 connected to the first positive electrode portion 121a and the negative electrode 122 is reduced. On the one hand, it avoids the distance between the first bending point 1212c and the negative electrode 122 being too close, and the distance between the first tab 1212 of the first positive electrode portion 121a and the negative electrode 122 being too small, which would increase the risk of the negative electrode 122 extending and contacting the aforementioned first tab 1212 when the battery expands, leading to a short circuit. On the other hand, it avoids the distance between the first bending point 1212c and the negative electrode 122 being too large, which would increase the space occupied by the positive electrode tab on one side in the second direction, resulting in a decrease in the energy density of the battery. At the same time, an excessively large distance between the first bending point 1212c and the negative electrode 122 may also exert a certain pulling effect on the first tab 1212 of a certain layer in the positive electrode tab, increasing the risk of the first tab breaking when subjected to external impact.

[0061] Furthermore, limiting d1 / L1 to a suitable range serves two purposes. First, it avoids d1 / L1 being too small, as either too small or too large, would cause the first bending point 1212c to be too close to the negative electrode 122, increasing the risk of contact between them. Alternatively, if L1 is too large, the redundant size of the first tab 1212 increases, which in turn increases the risk of the first tab 1212 deforming and contacting the edge of the negative electrode 122 or puncturing the separator 123 after a battery drop. Second, it avoids d1 / L1 being too large, as this would increase the space occupied by the positive electrode tab and the adapter 130 inside the battery, leading to a decrease in the battery's energy density. Conversely, if d1 / L1 is too large and L1 is too small, the bonding stability between the separators 123 in the composite region 1231 decreases, making it easier for the separators 123 in the composite region 1231 to open under external force during battery cycle expansion or drop tests, exposing the negative electrode 122 and increasing the risk of contact with the first tab 1212. Thus, by keeping d1 / L1 within a suitable range, it is beneficial to improve the energy density of the battery while reducing the risk of short circuit between the negative electrode 122 and the first tab 1212.

[0062] Furthermore, after the cell assembly 120 is packaged into the casing, it needs to be thermo-sealed. Since the hardness of the adapter 130 is greater than that of a single first tab 1212, pressure will be generated on the adapter 130 during sealing. The stress is transmitted through the adapter 130 and acts on the first tab 1212, causing the first tab 1212 to shift towards the cell assembly 120. The multiple first tabs 1212 under pressure move closer to the cell body as a whole, which reduces the distance between the edge of the negative electrode 122 on the side of the first positive electrode portion 121a facing the first wall 111 and the first tab 1212 of the first positive electrode portion 121a, resulting in a decrease in d1. This increases the risk of the outermost first tab 1212 contacting the edge of the negative electrode. By comprehensively limiting the range of d1 / L1, even when d1 decreases, the composite region 1231 still has sufficient protective length, which is beneficial to improving the safety of the battery.

[0063] refer to Figure 1 and Figure 2 In some embodiments, an overlap area 1311 is formed between the first connecting segment 1212b and the second connecting segment 131. At least a portion of the overlap area 1311 is provided with solder marks 1312. Exemplarily, the solder marks 1312 may be located in the partial overlap area 1311, or they may extend to cover the entire overlap area 1311. Alternatively, multiple solder marks 1312 may be spaced apart along the extension direction of the overlap area 1311, in which case the solder marks 1312 cover a portion of the overlap area 1311. Thus, welding is performed in the overlap area 1311 within the first connecting segment 1212b and the second connecting segment 131, forming a reliable electrical connection between the positive electrode tab and the adapter 130, while ensuring sufficient mechanical connection strength. By arranging the first connecting segment 1212b and the second connecting segment 131 in an overlapping manner, the contact area between them is increased, which helps to evenly distribute the current density, thereby reducing contact resistance and improving the rate performance of the battery.

[0064] The length L2 of the overlapping area 1311 along the length direction of the second connecting segment 131 satisfies: 0.8mm ≤ L2 ≤ 4mm. For example, L2 can be 0.8mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, or 4mm. On the one hand, this avoids the overlapping coverage area of ​​the overlapping area 1311 being too small, resulting in poor current carrying capacity between the positive electrode tab and the adapter 130. On the other hand, it also avoids the connection stability between the first connecting segment 1212b and the second connecting segment 131 being affected by insufficient overlapping area. On the other hand, to avoid the overlapping area 1311 being too large, during the aforementioned hot-press sealing process, the larger the overlapping area 1311, the greater the transmission effect of the adapter 130 and the compressive stress on the first tab 1212. At this time, the situation of the first tab 1212 squeezing into the battery body is more significant, and the interference and squeezing risk of the pushing effect between the first tab 1212 and the composite area 1231 of the separator 123 also increases. This will lead to a decrease in d1 or an increase in the pushing effect on the composite area 1231, increasing the risk of the separator 123 of the composite area 1231 being misaligned and exposing the negative electrode.

[0065] The length L3 of the solder mark 1312 along the length direction of the second connecting segment 131 satisfies: 0.3mm ≤ L3 ≤ 2mm. For example, L3 can be 0.3mm, 0.6mm, 0.9mm, 1.2mm, 1.5mm, 1.8mm or 2mm. Of course, L3 can also be other sizes, and this application does not limit this.

[0066] On the one hand, it avoids the solder mark 1312 being too small, which would result in insufficient connection strength between the positive electrode tab and the adapter 130. On the other hand, it avoids the solder mark 1312 being too large, as this would require more heat during soldering. A large amount of heat would be conducted to the cell assembly 120 through the overlap area 1311 along the first tab 1212, causing the composite area 1231 of the separator 123 to shrink under the influence of heat. This would reduce the size of L1, affecting the physical isolation effect of the composite area 1231 on the edge of the negative electrode 122, and increasing the risk of short circuit between the first tab 1212 and the edge of the negative electrode 122.

[0067] It should be noted that when multiple solder marks 1312 are provided in the overlapping area 1311, L3 in this embodiment is the sum of the lengths of the multiple solder marks 1312 in the extending direction of the overlapping area 1311.

[0068] The included angle β between the second connecting segment 131 and the third connecting segment 132 satisfies: 70°≤β≤130°. For example, β can be 70°, 80°, 90°, 100°, 110°, 120° or 130°. Of course, β can also be other sizes, and this application does not limit this.

[0069] The third connecting section 132 of the adapter 130 extends outside the housing 110. The second connecting section 131 and the third connecting section 132 form a bent structure. During hot-press sealing, the bent adapter 130 is subjected to external force, which transmits stress to the positive electrode tab. On the one hand, to avoid the included angle between the second connecting section 131 and the third connecting section 132 being too small, the second bending point 133 on the adapter 130 protrudes higher than the upper surface of the electrode assembly along the first direction. When the battery is subjected to external force, the external force on the adapter 130 is too large and is transmitted to the positive electrode tab. This causes the multiple first tabs 1212 to move closer to the cell assembly 120 or to deform more, and intensifies the lateral pushing effect on the thermal composite area 1231 of the separator 123. This causes the composite area 1231 to shrink inward, shift, or misalign, resulting in the negative electrode edge being exposed and short-circuiting with the first tab 1212. At the same time, avoiding an excessively large angle between the second connecting segment 131 and the third connecting segment 132 also avoids an excessively large length dimension of the adapter 130 along the second direction, reducing the space occupied by the adapter 130 on the battery head, which is beneficial to improving the energy density of the battery.

[0070] On the other hand, it is necessary to avoid the angle between the second connecting section 131 and the third connecting section 132 being too small, and to avoid stress concentration at the connection between the second connecting section 131 and the third connecting section 132, which would reduce fatigue strength and affect the structural stability of the adapter 130.

[0071] refer to Figure 1 and Figure 2 In some embodiments, a second bending point 133 is formed between the second connecting segment 131 and the third connecting segment 132. Along the first direction, the distance between the first bending point 1212c and the side surface of the cell assembly 120 near the second wall 112 is H1, and the distance between the first bending point 1212c and the second bending point 133 along the first direction is H2.

[0072] Understandably, in this embodiment, H1 is the straight-line distance between the first bending point 1212c and the second wall 112, and H2 is the perpendicular distance between the first bending point 1212c and the second bending point 133 along the first direction.

[0073] H1 < H2, meaning that in this embodiment, in the first direction, the second bending point 133 of the adapter 130 protrudes from the side of the cell assembly 120 along the thickness direction (first direction) toward the second wall 112. A gap is formed between the surface of the cell assembly 120 near the second wall 112 and the second wall 112, creating a certain space margin to accommodate the bent portion on the adapter 130 (i.e., the area near the second bending point 133). This ensures that the second connecting segment 131 is in a straight-line extension state, thereby preventing the solder 1312 between the second connecting segment 131 and the first connecting segment 1212b from being bent, which would reduce the peel strength and tensile strength of the connection between the positive electrode tab and the adapter 130, potentially leading to breakage of the positive electrode tab in extreme cases. Furthermore, this gap also provides a certain buffer space to match the expansion and deformation of the cell assembly 120 during battery charging and discharging, improving battery reliability.

[0074] Furthermore, H2-H1 ≤ 0.3 mm. For example, H2-H1 can be 0.1 mm, 0.2 mm, or 0.3 mm.

[0075] Generally, the thickness of the adapter 130 is greater than the thickness of a single first tab 1212. Under the condition that H1 < H2, during the battery fabrication and shaping process and hot pressing formation, when subjected to pressure along the first direction and / or the second direction, the adapter 130 protrudes from the upper surface of the cell assembly and is more susceptible to greater external pressure. This pressure is transmitted to the first tab 1212, causing it to deform or shift. At this time, the first tab 1212 of the first positive electrode portion 121a is more likely to come into contact with the negative electrode, leading to a short circuit. Therefore, it is necessary to further control the dimension of H2 exceeding H1 within a suitable range to ensure that the solder area 1312 between the positive electrode tab and the adapter 130 is not bent, while reducing the first tab 1212 coming into contact with the negative electrode and causing a short circuit.

[0076] refer to Figure 1 and Figure 2 In some embodiments, along the first direction, the positive electrode 121 includes a second positive electrode portion 121b near the second wall 112. The first tab 1212 of the second positive electrode portion 121b includes a second stacked segment 1212d and a fourth connecting segment 1212e connected to the second stacked segment 1212d. Along the second direction, the fourth connecting segment 1212e is located on the side of the second stacked segment 1212d away from the positive current collector 1211.

[0077] Understandably, in this embodiment, the second positive electrode portion 121b is the portion of the positive electrode 121 with the first tab 1212 closest to the second wall 112. The first positive electrode portion 121a and the second positive electrode portion 121b together constitute the two side boundary portions of the positive electrode 121 along the first direction with the first tab 1212. Similarly, for a wound battery cell, the outermost portion of the positive electrode 121 is generally a positive electrode single-sided area or a positive electrode empty foil area, without the first tab 1212. That is, in a wound battery cell, the second positive electrode portion 121b of the positive electrode 121 is not the outermost portion of the positive electrode 121 closest to the second wall 112, but rather the portion of the positive electrode 121 with the first tab 1212 closest to the second wall 112.

[0078] The connection between the second stacked segment 1212d and the fourth connecting segment 1212e forms a third bending point 1212f. Along the second direction, the interval between the third bending point 1212f and the edge of the negative electrode 122 is d2, where 0.7 ≤ d1 / d2 ≤ 1.3. For example, d1 / d2 can be 0.7, 0.8, 0.9, 1, 1.1, 1.2 or 1.3. Of course, d1 / d2 can also be other values, and this application does not limit them.

[0079] In this embodiment, d1 and d2 are the distances between the bending points of the two end tabs of the positive electrode tab along the first direction and the corresponding negative electrode plate 122, respectively. d1 / d2 reflects the degree of dispersion of several first tabs 1212 when the positive electrode tab is bent.

[0080] By keeping d1 / d2 within a suitable numerical range, the closer d1 / d2 is to 1, the more concentrated the several first tabs 1212 become, and the higher the stability of the positive tab. If the difference between d1 / d2 and 1 is too large (e.g., d1 / d2 < 0.7 or d1 / d2 > 1.3), the several first tabs 1212 become more dispersed, the stability of the positive tab is poor, and the first tabs 1212 are more prone to deformation and displacement when subjected to stress transmitted by the adapter 130, increasing the risk of short circuit due to contact with the negative electrode 122.

[0081] In some embodiments, at least one first tab 1212 in the positive electrode tab portion includes a bending section. The arrangement heights of the plurality of first tabs 1212 in the positive electrode tab portion along a first direction are different. When the stacked positive electrode tab portions are bent towards the first wall 111 along the first direction, a bending section is formed between the connection point of the first tab 1212 and the positive electrode plate 121 and the bending point of the positive electrode tab portion. Specifically, one first tab 1212 in the positive electrode tab portion may have a bending section (e.g., the first tab 1212 of the first positive electrode plate portion 121a), or multiple first tabs 1212 may have bending sections.

[0082] The bending section includes a first bending segment and a second bending segment. The angle between the first bending segment and the second bending segment is α, where 40°≤α≤180°. For example, α can be 40°, 45°, 50°, 60°, 70°, 80°, 100°, 120°, 140°, 160°, 166°, 170°, 180°, etc. α is used to characterize the degree of bending of the bending section. The smaller α is, the smaller the interval between the first bending segment and the second bending segment in the second direction. Correspondingly, the smaller the interval between the first electrode tab 1212 and the negative electrode 122, the greater the risk of short circuit between the first electrode tab 1212 and the negative electrode 122.

[0083] By ensuring the angle between the first and second bending segments is within a suitable range, on the one hand, it avoids the angle α between the first and second bending segments being too small, which would result in an excessively small gap between the first tab 1212 and the negative electrode 122, increasing the risk of a short circuit between the first tab 1212 and the negative electrode 122. On the other hand, it avoids the angle α between the first and second bending segments being too large, which would result in excessive redundancy at the head of the positive electrode tab, making it prone to deformation and occupying too much space, potentially causing the first tab 1212 to easily contact the negative electrode or reducing the energy density of the battery.

[0084] It should be noted that in some embodiments, the bending section may be located on the stacked section of the first electrode tab 1212. For example, at least one first electrode tab 1212 in the positive electrode tab portion includes a third stacked section and a fifth connecting section connected to the third stacked section. Along the second direction, the third stacked section is close to the positive electrode current collector, and the fifth connecting section is far away from the positive electrode current collector. The third stacked section includes a first bending section and a second bending section. The second bending section connects the first bending section and the fifth connecting section. The angle between the first bending section and the second bending section is α.

[0085] In another specific example, the first tab 1212 of the first positive electrode portion 121a may have a bent section. The first tab 1212 of the first positive electrode portion 121a has a first laminated section 1212a connected to the first positive electrode portion 121a. The first laminated section 1212a includes a lead-out end connected to the positive current collector of the first positive electrode portion 121a. The bent section is located between the first bending point 1212c and the lead-out end. Since the positive electrode tab is bent toward the first wall 111, a bent section is formed in the head space of the housing 110 that accommodates the positive electrode tab. The first bent section of the bent section is connected to the lead-out end, and the second bent section extends to the first bending point 1212c. The included angle between the first bent section and the second bent section is α.

[0086] refer to Figure 1 , Figure 2 and Figure 4In some embodiments, the third connecting segment 132 is provided with an adhesive component 134, which is used to seal the housing 110 and fix the adapter 130 to the housing 110, thereby improving the installation stability of the adapter 130 and ensuring the structural stability of the positive electrode tab connected to the adapter 130.

[0087] The positive electrode tab is connected to the adapter 130 to form a current guiding structure. Along the length of the current guiding structure, the distance between the end of the adhesive part 134 near the cell assembly 120 and the edge of the separator 123 is L4.

[0088] Understandably, the flow guiding structure is bent multiple times. L4 is the curved distance between the innermost boundary of the adhesive part 134 (closest to the cell assembly 120) and the edge of the separator 123 along the length of the flow guiding structure. In other words, if the adapter 130 and the first electrode 1212 are both in a straight extension state along the second direction (the adapter 130 and the positive electrode are overlapped and connected without bending), L4 is the straight distance between the end of the adhesive part 134 facing the cell assembly 120 and the edge of the separator 123 along the second direction.

[0089] Thus, in this embodiment, L4 can be measured in the following way:

[0090] After the battery is discharged to 3.0V, the structure containing the adhesive part 134 on the adapter 130 connected to the housing 110, the adapter 130 connected to the first tab 1212, and the first tab 1212 connected to the cell assembly 120 is disassembled. Then, after the bend of the first tab 1212 is straightened, the distance L4 from the adhesive part 134 to the separator 123 is measured with an optical instrument (such as CCD or 2.5D).

[0091] Understandably, the dimensions of d1, L1, and d2 mentioned above can all be measured using the methods described above.

[0092] The thickness of the cell assembly 120 along the first direction is T, where L4 ≤ T. That is, in the unfolded state, the gap between the adhesive part 134 and the edge of the separator 123 does not exceed the thickness of the cell assembly 120. In the battery of this application, the positive electrode tab and the adapter 130 form a current-conducting structure after bending, thereby ensuring that the height of the first electrode tab 1212 along the first direction after bending does not exceed the thickness edge of the cell assembly 120. This reduces the squeezing effect of the adapter 130 on the first electrode tab 1212 when subjected to external force, which helps to reduce the risk of short circuit between the first electrode tab 1212 and the negative electrode 122.

[0093] Since L4≤T, the distance between the root of the adapter 130 (the end of the second connecting segment 131 facing away from the third connecting segment 132) and the edge of the diaphragm 123 along the length of the flow-conducting structure is also limited. In other words, the size of the positive electrode tab outside the diaphragm 123 to the part on the first connecting segment 1212b other than the overlapping area 1311 (that is, the stacked area extending from the battery cell assembly 120, the front section of the positive electrode tab before bending) is not too large. This helps to prevent the first electrode tab 1212 from having too much redundancy at the head of the battery cell (that is, the first electrode tab 1212 can move a lot), reduce the shaking redundancy of the first electrode tab 1212, thereby reducing the degree and distance of displacement of the first electrode tab 1212, and reducing the risk of short circuit between the first electrode tab 1212 and the negative electrode 122.

[0094] In some embodiments, the negative electrode 122 includes a negative electrode active layer, which comprises a silicon-based material. Introducing a silicon-based material into the negative electrode is beneficial to improving the overall energy density of the battery. However, pure silicon has a large volume expansion rate during charging and discharging, which easily leads to particle pulverization and repeated rupture and regeneration of the solid electrolyte interphase (SEI), resulting in rapid capacity decay and shortened battery cycle life.

[0095] The mass content of silicon in the negative electrode active layer is 5%-70%. Based on the total mass of the negative electrode active layer, the mass content of silicon in the negative electrode active layer can be 5%, 10%, 20%, 30%, 40%, 50%, 60% or 70%. Of course, the mass content of silicon in the negative electrode active layer can also be other values, and this application does not limit this.

[0096] On the one hand, it avoids that the silicon content is too low, which would have a limited effect on improving the battery's energy density. On the other hand, it avoids that the silicon content is too high, which would cause the negative electrode 122 to expand severely after the battery is charged and discharged, and extend along its second direction, increasing the risk of short circuit when it comes into contact with the first tab 1212 of the positive electrode.

[0097] Silicon-based materials include at least one of silicon-carbon composite materials and silicon-oxygen composite materials. For example, silicon-based materials may include silicon-carbon composite materials (such as graphite, amorphous carbon, carbon nanotubes, etc.), which utilize the flexibility and conductivity of carbon to mitigate the volume change of silicon and improve the rate performance of the battery. Alternatively, silicon-based materials may also include silicon-oxygen composite materials, which have a lower volume expansion rate than pure silicon, higher initial efficiency, better cycle stability, and are beneficial to extending the battery's lifespan.

[0098] In this invention, the mass content of silicon in the negative electrode active layer can be tested using conventional methods in the art. For example, after discharging the battery to 0% SOC, the negative electrode sheet is disassembled and soaked in dimethyl carbonate (DMC) solvent for 12 hours, then rinsed with DMC solvent to remove lithium salts and other substances adhering to the negative electrode sheet. After drying, the negative electrode sheet is subjected to high-temperature treatment at 400°C in an inert atmosphere for 2 hours (e.g., in a tube furnace under nitrogen or argon atmosphere). The negative electrode active coating can then be peeled off from the negative electrode current collector, and the negative electrode active coating is collected as a test sample. Using a thermogravimetric analyzer (e.g., a TGA 550 thermogravimetric analyzer), the test sample amount is 5mg-15mg. Under an air or oxygen atmosphere, the temperature is increased from room temperature (25°C) to 900°C at a rate of 10°C / min, and held at 900°C for 40 minutes, so that the non-silicon components in the negative electrode active layer volatilize while silicon is fully oxidized to silicon dioxide. The remaining substance is the ash content of the negative electrode active coating. The mass content of silicon in the negative electrode active layer can be calculated based on the mass of ash. The calculation formula is as follows: based on the total mass of the negative electrode active layer, the mass content of silicon = 7 × mass of ash / (15 × mass of test sample).

[0099] According to some embodiments of the present invention, the volume average particle size Dv50 of the silicon-based material is 2μm-15μm. Exemplarily, the volume average particle size Dv50 of the silicon-based material can be 2μm, 3μm, 5μm, 6μm, 7μm, 9μm, 10μm, 11μm, 12μm, 14μm, or 15μm. Of course, the volume average particle size Dv50 of the silicon-based material can also be other values, and this application does not limit it.

[0100] Dv50 (median particle size) is a core parameter characterizing the particle size distribution of silicon-based material powders. For silicon-based anode materials, particle size directly affects their electrochemical performance and processing characteristics. If the particle size is too small, although it can alleviate the volume expansion stress of the anode and shorten the lithium-ion diffusion path, it will cause a sharp increase in specific surface area, making it easy to have large-area contact with the electrolyte and generate side reactions. Furthermore, the edge of the anode sheet 122 is cut during the electrode preparation process, and the edge is a high-curvature position. There is an electric field charge accumulation effect in the high-curvature position. The edge of the anode sheet 122 near the first tab 1212 is at the current collection end. The conductive path of the anode current collector is short and the potential gradient is large. Combined with the charge accumulation effect of the high curvature of the edge, the current density is large. Therefore, the side reactions at this position are more intense, and lithium plating is prone to occur. This can lead to local deformation of the edge of the anode sheet 122 near the first tab 1212, or lithium dendrites growing towards the positive tab near the separator 123, forming a bridging contact and exacerbating the short-circuit safety hazard.

[0101] If the particle size is too large, the lithium-ion diffusion path becomes longer, the rate performance of the battery decreases, and the volume expansion of large silicon-based materials during charging and discharging aggravates the local stress concentration at the edge, causing the negative electrode edge to warp and peel up, and increasing the risk of the warped area coming into contact with the first tab 1212.

[0102] By limiting the volume average particle size Dv50 of the silicon-based material to 2μm-15μm, the particle size distribution of the silicon-based particles is moderate, avoiding phenomena such as edge warping, powder shedding, and severe negative electrode expansion caused by excessively large particle size. It also avoids the problem of aggravated side reactions caused by excessively small particle size, which would reduce the electrical performance of the battery. While taking into account the rate performance of the battery, it improves the edge flatness and structural regularity of the negative electrode 122, reducing the risk of short circuit due to close contact between the edge of the negative electrode 122 and the first tab 1212.

[0103] In this application, the volume average particle size Dv50 of the silicon-based material can be tested using conventional testing methods in the art, such as laser particle size analysis. For example, it can be measured using a Malvern particle size analyzer.

[0104] According to some embodiments of the present invention, the sphericity of the silicon-based material is 0.7-1. Exemplarily, the sphericity of the silicon-based material can be 0.7, 0.8, 0.9 or 1. Of course, the sphericity of the silicon-based material can also be other values, and this application does not limit this.

[0105] Sphericity is a dimensionless parameter that measures how close particles are to ideal spheres. In electrode materials, higher sphericity means better flowability of spherical or near-spherical particles during slurry preparation and coating, making them easier to disperse uniformly, reducing agglomeration, and resulting in a denser, more uniform electrode coating. Compared to sheet-like, needle-like, or irregular particles, spherical particles have the smallest surface area for the same volume, which helps suppress electrolyte side reactions, reduce excessive SEI film formation and gas generation, and improve initial coulombic efficiency. During charge and discharge, silicon-based materials undergo volume expansion / contraction. Due to their isotropic geometry, spherical particles can distribute internal stress more evenly, reducing the risk of cracking and pulverization, and improving cycle stability and rate performance.

[0106] By limiting the sphericity of silicon-based materials to 0.7-1, the silicon-based materials have a certain degree of sphericity, which allows them to withstand volume changes more uniformly during lithium insertion / extraction, reducing the breakage of silicon-based materials and improving the cycle life and rate performance of batteries.

[0107] In this invention, the sphericity of silicon-based materials can be tested using conventional methods in the art. For example, using image processing software, at least 10 silicon-based material particles are selected from a scanning electron microscope (SEM) image of silicon-based materials at a certain magnification (e.g., 2500x), and the perimeter and area of ​​each particle are measured. The perimeter equivalent radius r1 and area equivalent radius r2 of each particle are calculated respectively, and the sphericity is r2 / r1. The average value is then taken to obtain the sphericity of the silicon-based material.

[0108] refer to Figure 5 In some embodiments, the positive electrode 121, the negative electrode 122 and the separator 123 are wound to form a cell assembly 120. That is to say, the cell assembly 120 in this embodiment is a wound cell.

[0109] The positive electrode 121 has a first surface 121c and a second surface 121d. The first surface 121c faces the winding center, and the second surface 121d faces away from the winding center. That is, the first surface 121c forms the inner surface of the positive electrode 121, and the second surface 121d forms the outer surface of the positive electrode 121.

[0110] The first surface 121c is provided with a first positive electrode active layer 121e, and the second surface 121d is provided with a second positive electrode active layer 121f. The areal density of the first positive electrode active layer 121e is N1, and the areal density of the second positive electrode active layer 121f is N2, where 0.89 ≤ N1 / N2 ≤ 0.99. For example, N1 / N2 can be 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, or 0.99. Of course, N1 / N2 can also be other values, and this application does not limit them.

[0111] Due to the winding geometry, the radius of curvature of the first surface 121c is small, while that of the second surface 121d is large, resulting in greater compressive stress on the first positive electrode active layer 121e. Since 0.89 ≤ N1 / N2 ≤ 0.99, meaning N1 < N2, the areal density of the first positive electrode active layer is less than that of the second positive electrode active layer. This helps reduce the compaction of the first positive electrode active layer 121e, decreases its internal stress, improves electrode flexibility, and reduces the risk of cracking and powder shedding in the first positive electrode active layer 121e, thereby lowering the risk of lithium plating and micro-short circuits in the battery.

[0112] Meanwhile, limiting the ratio of the two to a suitable range reduces the risk of lithium plating in the negative electrode active layer corresponding to the first positive electrode active layer 121e near the winding center. This avoids N1 / N2 being too large, causing the NP ratio (N / P ratio is the negative electrode capacity per unit area / positive electrode capacity per unit area) between the first positive electrode active layer 121e near the winding center and its corresponding negative electrode active layer to be less than the NP ratio between the second positive electrode active layer 121f away from the winding center and its corresponding negative electrode active layer. This leads to a local NP ratio imbalance, resulting in local lithium plating in the negative electrode, which in turn causes the overall battery to expand significantly, increasing the extension of the negative electrode sheet 122. This results in the edge of the negative electrode sheet 122 being closer to the first tab 1212, making it more prone to short circuits. On the other hand, it avoids N1 / N2 being too small, causing the areal density of the first positive electrode active layer 121e to be too low, reducing the positive electrode active material on the positive electrode sheet 121, and thus reducing the energy density of the battery.

[0113] N1 and N2 can be measured in the following directions:

[0114] The extracted positive electrode sample 121 was immersed and rinsed in dimethyl carbonate solution to remove residual lithium salts (such as lithium hexafluorophosphate) from the surface. The immersion and rinsing were repeated 2 to 3 times, and then the sample was placed in a petri dish to air dry or vacuum dry.

[0115] Using a punching machine, punch several small discs (8 mm in diameter) from the cleaned and dried positive electrode sample 121, and record the area of ​​each disc. Weigh each small disc to determine its total weight.

[0116] The first positive electrode active layer 121e and the second positive electrode active layer 121f on the small disc are scraped off sequentially, and the small disc is weighed after each scraping. The weight of the first positive electrode active layer 121e is the difference between the total weight of the small disc and the weight of the small disc after scraping off the first positive electrode active layer 121e, and the weight of the second positive electrode active layer 121f is the difference between the weight of the small disc after scraping off the first positive electrode active layer 121e and the weight of the small disc after scraping off the second positive electrode active layer 121f.

[0117] The areal density N1 of the first positive electrode active layer 121e is the weight of the first positive electrode active layer 121e divided by the area of ​​the small disc, and the areal density N2 of the second positive electrode active layer 121f is the weight of the second positive electrode active layer 121f divided by the area of ​​the small disc.

[0118] In a specific example, the thickness of the battery casing in this application is 50-200 μm.

[0119] The active material in the positive electrode active material layer includes one or more of lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese, lithium nickel cobalt aluminum, lithium manganese oxide, and lithium-rich manganese-based lithium.

[0120] The negative electrode active material layer includes, but is not limited to, one or more of the following: natural graphite, artificial graphite, mesophase carbon microspheres, lithium titanate, silicon negative electrode, silicon-carbon negative electrode, and alloy negative electrode. The negative electrode active material layer also includes a negative electrode adhesive, which is mainly a styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), or polyacrylic acid (PAA) adhesive.

[0121] The positive electrode active material layer also includes a positive electrode binder, which is mainly a polyvinylidene fluoride (PVDF) type binder.

[0122] The conductive agent includes at least one of conductive carbon black, Ketjen black, single-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0123] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A battery, characterized in that, include: Housing (110), cell assembly (120) and adapter (130). The housing (110) includes a receiving cavity (110a) for accommodating a cell assembly (120). The housing (110) includes a first wall (111) and a side wall surrounding the first wall (111). The first wall (111) and the side wall surrounding the first wall (111) together form the receiving cavity (110a). Along a first direction, the housing (110) also includes a second wall (112) disposed opposite to the first wall (111). The battery cell assembly (120) includes a positive electrode (121), a negative electrode (122), and a separator (123) disposed between the positive electrode (121) and the negative electrode (122). Along the first direction, the separator (123) is disposed on both sides of the negative electrode (122). Along the second direction, the edges of two adjacent separators (123) extend beyond the edge of the negative electrode (122). At least a portion of the edges of adjacent separators (123) are bonded together to form a composite region (1231). The length L1 of the composite region (1231) along the second direction satisfies: 0.3mm ≤ L1 ≤ 2.2mm. The positive electrode plate (121) includes a positive current collector (1211), and the positive electrode plate (121) also includes a plurality of first tabs (1212) extending outward from one side of the positive current collector (1211); the plurality of first tabs (1212) are stacked to form a positive electrode tab portion, the positive electrode tab portion is bent toward the first wall (111) along a first direction, and along the first direction, the positive electrode plate (121) includes a first positive electrode plate portion (121a) near the first wall (111), and the first tab (1212) of the first positive electrode plate portion (121a) includes a first stacked segment (1212a). And a first connecting segment (1212b) connected to the first stacked segment (1212a), along the second direction, the first connecting segment (1212b) is located on the side of the first stacked segment (1212a) away from the positive current collector (1211), the connection between the first stacked segment (1212a) and the first connecting segment (1212b) forms a first bending point (1212c), along the second direction, the distance d1 between the edge of the negative electrode sheet (122) near the first bending point (1212c) and the first bending point (1212c) satisfies: 0.2mm≤d1≤2mm; The adapter (130) includes a second connecting segment (131) and a third connecting segment (132) formed by bending, the first connecting segment (1212b) being connected to the second connecting segment (131), and the third connecting segment (132) extending out of the housing (110). Among them, L1 and d1 satisfy the following condition: 0.1≤d1 / L1≤3.

2. The battery according to claim 1, characterized in that, An overlapping area (1311) is formed between the first connecting segment (1212b) and the second connecting segment (131), and a solder mark (1312) is provided on at least part of the overlapping area (1311). The length L2 of the overlapping area (1311) along the length direction of the second connecting segment (131) satisfies: 0.8mm ≤ L2 ≤ 4mm; and / or, The length L3 of the solder mark (1312) along the length direction of the second connecting segment (131) satisfies: 0.3mm ≤ L3 ≤ 2mm; and / or, The included angle β between the second connecting segment (131) and the third connecting segment (132) satisfies: 70°≤β≤130°.

3. The battery according to claim 1, characterized in that, A second bending point (133) is formed between the second connecting segment (131) and the third connecting segment (132); along the first direction, the distance between the first bending point (1212c) and the side surface of the cell assembly (120) near the second wall (112) is H1, and the distance between the first bending point (1212c) and the second bending point (133) along the first direction is H2, H1 < H2, and H2 - H1 ≤ 0.3 mm.

4. The battery according to claim 1, characterized in that, Along the first direction, the positive electrode (121) includes a second positive electrode portion (121b) near the second wall (112). The first tab (1212) of the second positive electrode portion (121b) includes a second stacked segment (1212d) and a fourth connecting segment (1212e) connected to the second stacked segment (1212d). Along the second direction, the fourth connecting segment (1212e) is located on the side of the second stacked segment (1212d) away from the positive current collector (1211). A third bending point (1212f) is formed at the connection between the second stacked segment (1212d) and the fourth connecting segment (1212e). Along the second direction, the interval between the third bending point (1212f) and the edge of the negative electrode (122) is d2, where 0.7≤d1 / d2≤1.

3.

5. The battery according to claim 1, characterized in that, At least one first electrode tab (1212) in the positive electrode tab portion includes a bending section, the bending section including a first bending segment and a second bending segment, the angle between the first bending segment and the second bending segment being α, 40°≤α≤180°.

6. The battery according to claim 1, characterized in that, The positive electrode tab is connected to the adapter (130) to form a flow guiding structure. The third connecting section (132) is provided with an adhesive (134). Along the length direction of the flow guiding structure itself, the distance between the end of the adhesive (134) near the cell assembly (120) and the edge of the separator (123) is L4. The thickness of the cell assembly (120) along the first direction is T, and L4≤T.

7. The battery according to claim 1, characterized in that, The negative electrode (122) includes a negative electrode active layer, the negative electrode active layer comprising a silicon-based material, wherein the mass content of silicon in the negative electrode active layer is 5%-70%; and / or, The silicon-based material includes at least one of silicon-carbon composite materials and silicon-oxygen composite materials.

8. The battery according to claim 7, characterized in that, The volume average particle size Dv50 of the silicon-based material is 2μm-15μm.

9. The battery according to claim 8, characterized in that, The sphericity of the silicon-based material is 0.7-1.

10. The battery according to claim 1, characterized in that, The positive electrode (121), the negative electrode (122), and the separator (123) are wound to form the battery cell assembly (120). The positive electrode (121) has a first surface (121c) facing the winding center of the battery cell assembly (120) and a second surface (121d) facing away from the winding center of the battery cell assembly (120). The first surface (121c) is provided with a first positive active layer (121e), and the second surface (121d) is provided with a second positive active layer (121f). The areal density of the first positive active layer (121e) is N1, and the areal density of the second positive active layer (121f) is N2, with 0.89≤N1 / N2≤0.99.

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